I have plenty of switching power supply units. It seems that they have noise issues. But my computer is silent and can produce good sound. And so do newer commercial DVD players. So what is the real problem here?

Recently I took out a switching power supply which is also used to power up computer monitor. I guess the voltage and current is suitable for at least providing B+ for a tube preamp. Anybody know if this is possible or not?

SMPS and so called Iron PSU's all get built for a cost which means there either good ok or rubbish, that said I have a pre-amp which runs from an smps and it is very clean. I think it all depends what your preference is and what you can get.

There is no reason a well designed SMPS can't be as good as a conventional PSU. Having said that I wouldn't say that computer smps's are always good examples of state of the art electronics.

But I have heard of people modifying them to supply other voltage/current then what they were designed to.

I think it really becomes a personal taste aspect and what your comfortable wit.

I did some R&D on SMPS for automotive tube audio use and found it as good as a SS bench linear supply.

The only think to remember is careful shielding and proper bypassing. I double-shielded (with gap to avoid a ground-loop), looped the wire a couple of times through an RFI toroid and finally out through feedthrough capacitors.

Originally posted by rascal101 The noise from an SMPS is just too high to be acceptable for audio. Ripple & Noise, conducted and radiated emi, switching noise etc.

This is a bit of a sweeping statement, aka generalisation.

SMPSs, like all PSUs, are built to spec. Most digital systems can tolerate a certain amount of noise at 50kHz etc, but not so for audio. So, audio SMPSs are heavily filtered and are run at non-audio frequencies. I have built many many SMPSs, a couple of which I use for valve audio use. These are not hack designs, but are high-end systems.

Basically, for the average person, its far easier to build a quiet non-SMPS that an SMPS system - SMPSs are tricky to get right. However, if you do get it right, they are cheap, small, light, highly efficient and very effective. Noise is barely measurable on a good system.

When I use an SMPS for audio use, I use good filters on both input and output e.g. MuRata BNP002-03 and encase the SMPS in a shielding box (as used for small RF projects - you can also use a box made from soldered pieces of single or double sided PCB - another Ham Radio trick).

I design SMPS for a living and yes if you use the standard run of the mill designs used in the last 20 years, you will not get good performance in audio...
I have designed switchers that switch as high as 2 Mhz and and produce little noise...
ALso , the use of quasi-resonant/resonant SMPS circuits are very low with EMI ....
There is a place for SMPS in audio, I would recomend switching above 450kHz and also using a resonant topology...

I guess you are familiar with the Vicor units, which I think are quasi-resonant (or zero-current switching). I have used a few (the 150W 2nd generation units) in audio designs with good results, but that may have been luck .

What is your opinion on the Vicors for audio use? They also have a RAM (Ripple Attenuation Module) available to further decrease output noise by some 20dB, but the final price gets steep so I am not sure it would be worthwhile.

Jan Didden

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Chris, further to Jan's post, can you name a few brands of switchers you think give good performance for audio use? Would much appreciate your opinion. I've been looking on the internet, but cannot seem to latch onto proper figures of merit to guide my search.